This invention relates to coating compositions for forming mar and weather-resistant protective coatings on plastic substrates, typically polycarbonate resin substrates, a method for coating plastic substrates with the coating compositions, and coated articles having coatings thereof.
As glazing substitutes, shatterproof or highly shatter resistant transparent materials have been widely utilized for these decades. For example, plastic substrates, especially polycarbonate resins have superior transparency, impact resistance and heat resistance and are currently used as structural members instead of glass in a variety of applications including building and vehicle windows and instrument covers.
The polycarbonate resins, however, are inferior to glass in surface properties such as mar resistance and weather resistance. It is desired to improve the surface properties of polycarbonate resin parts. Nowadays, polycarbonate resin parts for use as vehicle windows and acoustic barrier walls along highways are required to withstand more than 10 years of weathering.
Known means for improving the weather resistance of polycarbonate resin parts include the lamination of a weather resistant acrylic resin film on the surface of a polycarbonate resin substrate and the formation of a ultraviolet absorber-containing resin layer on the resin surface, for example, by co-extrusion.
For improving the mar resistance of polycarbonate resin parts, it is known to coat thermosetting resins such as polyorganosiloxanes and melamine resins and to coat photo-curable resins such as polyfunctional acrylic resins.
As to the manufacture of transparent articles having both weather resistance and mar resistance, JP-A 56-92059 and JP-A 1-149878 disclose ultraviolet-absorbing transparent substrates having a primer layer loaded with a large amount of UV absorber added and a protective coating of colloidal silica-containing polysiloxane paint overlying the primer layer.
However, several problems arise with this approach. The addition of a large amount of UV absorber can adversely affect the adhesion to the substrate. During heat curing step, the UV absorber can volatilize off. On outdoor use over a long period of time, the UV absorber will gradually bleed out, causing whitening. From the mar resistance standpoint, it is impossible to add a large amount of UV absorber to the protective coating of colloidal silica-containing polysiloxane.
On the other hand, Japanese Patent Nos. 2,938,458 and 2,924,018, JP-A 11-286652 and JP-A 10-324827 attempt to enhance the curing properties and weather and abrasion resistance of coating compositions by adding thereto titanium chelate compounds or partial hydrolyzates thereof which play the catalytic role of promoting cure. Undesirably, these attempts rather detract from crack resistance by reason of over-curing, and tend to adversely affect storage stability.
An object of the invention is to provide a coating composition and method for forming a protective coating having improved mar and weather resistance. Another object is to provide a coated article having a mar and weather-resistant coating.
The inventors have found that a coating composition capable of achieving the above objects is obtained by blending an organosilicon compound having a hydrolyzable group-bearing silyl group with a hydrolytic condensate (sometimes referred to as final reaction product) of a reaction product and/or a mixture of a xcex2-diketone with a mixture (b-1) containing a titanium tetraalkoxide and a metal alkoxide of the formula: M(OR)n wherein M is at least one metal selected from among Zr, Fe, Al, Zn, In, Cu, Si, Sn, W, and Mg, n is the valence of the metal, and R is an alkyl group of 1 to 10 carbon atoms or hydrogen.
Studying a coating composition for improving the mar and weather resistance of molded parts of thermoplastic resins such as polycarbonate, the inventors have discovered that when the final reaction product is added to the organosilicon compound, the resulting composition remains very stable over a long term. Especially the final reaction product is (1) the reaction product obtained by reacting in a solvent the mixture (b-1) of the titanium tetraalkoxide as a main component and the metal alkoxide with a xcex2-diketone, followed by hydrolytic condensation, or (2) the reaction product obtained by subjecting the mixture (b-1) of the titanium tetraalkoxide as a main component and the metal alkoxide to hydrolytic condensation in a solvent containing a xcex2-diketone. Unlike customary titanium oxide sol, the final reaction product is soluble in solvents, does not settle with the lapse of time, and remains stable in the mixture. When a coating is formed from the composition, very good transparency is provided as compared with the titanium oxide sol. Since the final reaction product takes a microparticulate structure and has xcex2-diketone ligands left on particle surfaces, it imparts lubricity to the coating surface, significantly improving abrasion resistance as compared with the conventional titanium oxide sol-added coatings. Moreover, the final reaction product can act as a crosslinking catalyst to achieve nearly full-cure crosslinkage even under moderate curing conditions, leaving few uncrosslinked portions. Crack resistance is improved since the undesirable phenomenon that micro-cracks generate as a result of slow progress of crosslinking with time is eliminated.
Additionally, the final reaction product itself has a ultraviolet radiation absorbing capability, which eliminates the addition of or reduces the amount of an organic UV absorber, thereby removing the detrimental effects by bleeding-out of such absorber. Since there is no loss of UV absorbing capability which is otherwise caused by decomposition of organic UV absorbers, satisfactory weather resistance is kept over a long period of time. Continuing further study on the ratio and amounts of distinct components in the coating composition, the inventors has arrived at the present invention.
In one aspect, the invention provides a coating composition as defined below.
I) A coating composition comprising
(A) 100 parts by weight of an organosilicon compound having a hydrolyzable group-bearing silyl group, and
(B) 0.1 to 50 parts by weight of a hydrolytic condensate of a reaction product and/or a mixture of a xcex2-diketone with a mixture (b-1) containing a titanium tetraalkoxide and a metal alkoxide of the formula: M(OR)N wherein M is at least one metal selected from the group consisting of Zr, Fe, Al, Zn, In, Cu, Si, Sn, W, and Mg, n is the valence of the metal, and R is an alkyl group of 1 to 10 carbon atoms or hydrogen.
II) The coating composition of I wherein component (A) is a silane compound of the formula (1):
R3aSi(R4)4-axe2x80x83xe2x80x83(1) 
wherein R3 is an alkyl, aryl, halogenated alkyl, halogenated aryl or alkenyl group of 1 to 10 carbon atoms or an organic group having an epoxy, (meth)acryloxy, mercapto, amino or cyano group, R4 is an alkoxy, alkenyloxy, acyloxy or alkoxyalkoxy group of 1 to 10 carbon atoms, and xe2x80x9caxe2x80x9d is 0, 1 or 2, and/or a hydrolyzate thereof.
III) The coating composition of I wherein component (A) is an organic copolymer of an alkoxysilyl group-containing acrylic and/or vinyl monomer and another monomer copolymerizable therewith, the content of the alkoxysilyl group-containing acrylic and/or vinyl monomer in the organic copolymer being 0.1 to 50% by weight.
IV) The coating composition of any one of I to III wherein component (B) is a hydrolytic condensate obtained by reacting in a solvent the mixture (b-1) with a xcex2-diketone of the general formula: R1COCH2COR2 wherein R1 and R2 are alkyl groups of 1 to 6 carbon atoms and may be the same or different, followed by hydrolytic condensation.
V) The coating composition of any one of I to III wherein component (B) is a hydrolytic condensate obtained by subjecting the mixture (b-1) to hydrolytic condensation in a solvent containing a xcex2-diketone of the general formula: R1COCH2COR2 wherein R1 and R2 are alkyl groups of 1 to 6 carbon atoms and may be the same or different.
VI) The coating composition of any one of I to V wherein the amount of the xcex2-diketone is 0.5 to 2 molar equivalents based on the mixture (b-1).
VII) The coating composition of any one of I to VI wherein the amount of water used in hydrolytic condensation is 3.1 to 15 molar equivalents based on the mixture (b-1).
VIII) The coating composition of any one of I to VII wherein the mixture (b-1) contains 100 parts by weight calculated as TiO2 of the titanium tetraalkoxide and 0.01 to 50 parts by weight calculated as oxide of the metal alkoxide.
IX) The coating composition of any one of I to VIII wherein component (B) is microparticulate metal oxide having a mean particle size of up to 100 nm and bearing xcex2-diketone groups.
X) The coating composition of any one of I to IX wherein component (B) is capable of absorbing ultraviolet radiation having a wavelength of up to 350 nm.
XI) The coating composition of any one of I to X, further comprising (C) 0.1 to 100 parts by weight of a microparticulate inorganic oxide containing at least one atom selected from cerium and zinc and capable of absorbing radiation having a wavelength of up to 400 nm.
XII) The coating composition of any one of I to XI, further comprising (D) 1 to 200 parts by weight of colloidal silica.
XIII) The coating composition of any one of I to XII, further comprising 0.1 to 10 parts by weight of a photo-stabilizer having at least one cyclic hindered amine structure in a molecule.
It is understood that the coating composition of III is suitable as a primer whereas the coating composition of II is suitable to directly apply onto a substrate or to apply as a topcoat onto a primer coating.
In another aspect, the invention provides a coated article, that is, an article having a protective coating with improved weather resistance and abrasion resistance, the coating being formed from the coating composition defined above.
In a further aspect, the invention provides a coating method as defined below as well as a coated article obtained by the coating method.
XIV) A method for providing a plastic substrate with a weather and abrasion-resistant coating, comprising the steps of:
(i) applying an organic solvent solution of the coating composition of III onto a plastic substrate,
(ii) evaporating the organic solvent and curing the coating to form a primer layer,
(iii) applying the coating composition of II onto the primer layer, and
(iv) heating the coating of the coating composition at a temperature of 50 to 140xc2x0 C. for curing.
XV) A method for providing a plastic substrate with a weather and abrasion-resistant coating, comprising the steps of:
(i) applying an organic solvent solution of the coating composition of III onto a plastic substrate,
(ii) evaporating the organic solvent and curing the coating to form a primer layer,
(iii) applying a colloidal silica-laden organopolysiloxane composition onto the primer layer, the organopolysiloxane composition comprising a hydrolyzate or co-hydrolyzate of an alkoxysilane of the following general formula (2):
R7eSi(OR8)4-exe2x80x83xe2x80x83(2) 
wherein R7 is selected from the class consisting of an alkyl group, aryl group, halogenated alkyl group, halogenated aryl group and alkenyl group of 1 to 10 carbon atoms, and an organic group having an epoxy, (meth)acryloxy, mercapto, amino or cyano group, R8 is hydrogen or a monovalent organic group of 1 to 10 carbon atoms, and x is equal to 0, 1 or 2, and colloidal silica, and
(iv) heating the coating of the organopolysiloxane composition at a temperature of 50 to 140xc2x0 C. for curing.
The plastic substrate is typically comprised of a polycarbonate resin.
In a first embodiment of the invention, the coating composition contains
(A) 100 parts by weight of an organosilicon compound having a hydrolyzable group-bearing silyl group, and
(B) 0.1 to 50 parts by weight of a hydrolytic condensate of a reaction product and/or a mixture of a xcex2-diketone with a mixture (b-1) containing a titanium tetraalkoxide and a metal alkoxide of the formula: M(OR)n wherein M is at least one metal selected from the group consisting of Zr, Fe, Al, Zn, In, Cu, Si, Sn, W, and Mg, n is the valence of the metal, and R is an alkyl group of 1 to 10 carbon atoms or hydrogen.
The organosilicon compound having a hydrolyzable group-bearing silyl group (A) is preferably component (A-1) or (A-2) shown below, though not limited thereto.
(A-1) a silane compound of the formula (1):
R3aSi(R4)4-axe2x80x83xe2x80x83(1) 
wherein R3 is an alkyl, aryl, halogenated alkyl, halogenated aryl or alkenyl group of 1 to 10 carbon atoms or an organic group having an epoxy, (meth)acryloxy, mercapto, amino or cyano group, R4 is an alkoxy, alkenyloxy, acyloxy or alkoxyalkoxy group of 1 to 10 carbon atoms, and xe2x80x9caxe2x80x9d is 0, 1 or 2, and/or a hydrolyzate thereof.
(A-2) an organic copolymer of an alkoxysilyl group-containing acrylic and/or vinyl monomer and another monomer copolymerizable therewith, the content of the alkoxysilyl group-containing acrylic and/or vinyl monomer in the organic copolymer being 0.1 to 50% by weight.
Now the components (A-1) and (A-2) are described in detail.
Component (A-1)
It is a silane compound of formula (1) and/or a (partial) hydrolyzate thereof.
R3aSi(R4)4-axe2x80x83xe2x80x83(1) 
Herein R3 stands for alkyl groups, aryl groups, halogenated alkyl groups, halogenated aryl groups or alkenyl groups of 1 to 10 carbon atoms, or organic groups having an epoxy, (meth)acryloxy, mercapto, amino or cyano group. Examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, hexyl, decyl and cyclohexyl; aryl groups such as phenyl and phenethyl; halogenated alkyl groups such as 3-chloropropyl, 3,3,3-trifluoropropyl, and 3,3,4,4,5,5,6,6,6-nonafluorohexyl; halogenated aryl groups such as p-chlorophenyl; alkenyl groups such as vinyl, allyl, 9-decenyl and p-vinylbenzyl; epoxy group-containing organic groups such as 3-glycidoxypropyl, xcex2-(3,4-epoxy-cyclohexyl)ethyl and 9,10-epoxydecyl; (meth)acryloxy group-containing organic groups such as xcex3-methacryloxypropyl and xcex3-acryloxy; mercapto group-containing organic groups such as xcex3-mercaptopropyl and p-mercaptomethylphenylethyl; amino group-containing organic groups such as xcex3-aminopropyl and (xcex2-aminoethyl)-xcex3-aminopropyl; and cyano group-containing organic groups such as xcex2-cyanoethyl.
R4 stands for alkoxy, alkenyloxy, acyloxy or alkoxyalkoxy groups of 1 to 10 carbon atoms, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isopropenoxy and methoxyethoxy.
The letter xe2x80x9caxe2x80x9d is equal to 0, 1 or 2. The silane compound used herein functions as a binder having a bonding ability.
Illustrative, non-limiting, examples of the silane compounds that satisfy the above conditions include
trialkoxy or triacyloxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, methyltris(2-methoxyethoxy) silane, methyltriacetoxysilane, methyltripropoxysilane, methyltriisopropenoxysilane, methyltributoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyltris(2-methoxyethoxy)silane, vinyltriisopropenoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriacetoxysilane, xcex3-chloropropyltrimethoxysilane, xcex3-chloropropyltriethoxysilane, xcex3-chloropropyltripropoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, xcex3-glycidoxypropyltrimethoxysilane, xcex3-glycidoxypropylmethyldimethoxysilane, xcex3-glycidoxypropyltriethoxysilane, xcex3-glycidoxypropylmethyldiethoxysilane, xcex3-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, xcex3-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, xcex2-(3,4-epoxycyclohexyl)-ethylmethyldiethoxysilane, xcex3-methacryloxypropyltrimethoxysilane, xcex3-acryloxypropyltrimethoxysilane, xcex3-aminopropyltrimethoxysilane, xcex3-aminopropyltriethoxysilane, xcex3-mercaptopropyltrimethoxysilane, xcex3-mercaptopropyltriethoxysilane, N-(xcex2-aminoethyl)-xcex3-aminopropyltrimethoxysilane, and xcex2-cyanoethyltrimethoxysilane;
dialkoxysilanes or diacyloxysilanes such as dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldi(2-methoxyethoxy)silane, dimethyldiacetoxysilane, dimethyldipropoxysilane, dimethyldiisopropenoxysilane, dimethyldibutoxysilane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, vinylmethyldiacetoxysilane, vinylmethyldi(2-methoxyethoxy)silane, vinylmethyldiisopropenoxysilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane, phenylmethyldiacetoxysilane, xcex3-glycidoxypropylmethyldimethoxysilane, xcex3-glycidoxypropylmethyldiethoxysilane, xcex3-glycidoxypropylmethyldipropoxysilane, 3,3,3-trifluoropropylmethyldimethoxysilane, xcex3-methacryloxypropylmethyldimethoxysilane, xcex3-acryloxypropylmethyldimethoxysilane, xcex3-aminopropylmethyldimethoxysilane, xcex3-aminopropylmethyldiethoxysilane, xcex3-mercaptopropylmethyldimethoxysilane, xcex3-mercaptopropylmethyldiethoxysilane, N-(xcex2-aminoethyl)-xcex3-aminopropylmethyldimethoxysilane, and xcex3-cyanoethylmethyldimethoxysilane; and
tetraalkoxysilanes such as methyl silicate, ethyl silicate, n-propyl silicate, n-butyl silicate, sec-butyl silicate, and t-butyl silicate.
Partial or complete hydrolyzates of these silane compounds are also useful. These silane compounds and/or hydrolyzates thereof may be used alone or in admixture of two or more.
The (partial) hydrolyzates of the above silane compounds are obtained, for example, by adding water to a lower alcohol solution of the silane compound in the presence of an acid catalyst and effecting hydrolysis. Exemplary lower alcohols are methanol, ethanol, isopropanol and butanol. Solvents compatible with these alcohols include ketones such as acetone and acetylacetone, esters such as ethyl acetate and isobutyl acetate, and ethers such as propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, and diisopropyl ether.
Component (A-2)
It is an organic copolymer resin of an alkoxysilyl group-containing acrylic and/or vinyl monomer and another monomer copolymerizable therewith. Owing to the alkoxysilyl groups introduced, the coating composition is improved in adhesion to substrates. Crosslinking of alkoxysilyl groups together improves heat resistance and imparts durability. If the content of the alkoxysilyl group-containing monomer is less than 0.1% by weight, heat resistance and durability are not improved. If the content of the alkoxysilyl group-containing monomer is more than 50% by weight, the copolymer would become too hard, losing adhesion. Therefore, the content of the alkoxysilyl group-containing acrylic and/or vinyl monomer is 0.1 to 50%, preferably 1 to 40%, and more preferably 5 to 30% by weight based on the total weight combined with the other monomer.
Examples of the alkoxysilyl group-containing acrylic monomer include 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, 3-acryloxypropylmethyldimethoxysilane, 3-acryloxypropylmethyldiethoxysilane, 3-methacryloxymethyltrimethoxysilane, 3-methacryloxymethyltriethoxysilane, 3-methacryloxymethylmethyldimethoxysilane, 3-methacryloxymethylmethyldiethoxysilane, 3-acryloxymethyltrimethoxysilane, 3-acryloxymethyltriethoxysilane, 3-acryloxymethylmethyldimethoxysilane, and 3-acryloxymethylmethyldiethoxysilane. Of these, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, and 3-acryloxypropylmethyldimethoxysilane are preferred for ease of handling, crosslinked density and reactivity.
Examples of the alkoxysilyl group-containing vinyl monomer include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, vinylmethylbis(2-methoxyethoxy)silane, 3-vinyloxypropyltrimethoxysilane, 3-vinyloxypropyltriethoxysilane, 3-vinyloxypropylmethyldimethoxysilane, 3-vinyloxypropylmethyldiethoxysilane, styryltrimethoxysilane, styryltriethoxysilane, styrylmethyldimethoxysilane, and styrylmethyldiethoxysilane. Of these, vinyltrimethoxysilane, vinyltriethoxysilane, and 3-vinyloxypropyltrimethoxysilane are preferred for ease of handling and reactivity.
Examples of the other monomer copolymerizable with the alkoxysilane monomer include alkyl methacrylates such as methyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate; alkyl acrylates such as methyl acrylate, ethyl acrylate, and butyl acrylate; vinyl ethers such as glycidyl methacrylate, acrylamide, acrylonitrile, vinyl acetate, ethyl vinyl ether, butyl vinyl ether, and hexyl vinyl ether; styrene and ethylene glycol dimethacrylate; methacrylic group-containing benzotriazoles serving as a UV absorber such as 2-(2xe2x80x2-hydroxy-5xe2x80x2-methacryloxyethylphenyl)-2H-benzotriazole; and methacrylic group-containing hindered amines serving as a photo-stabilizer such as 2,2,6,6-tetramethyl-4-piperidinyl methacrylate and 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate. It is noted that compounds having a group capable of reacting with the alkoxysilyl group, for example, 2-hydroxyethyl methacrylate are undesirable since they can cause the coating composition to change with time, typically thickening or gelling. Preferred for this reason are those compounds free of a hydroxyl or similar group capable of reacting with the alkoxysilyl group.
The organic copolymer is a copolymer of the alkoxysilyl group-containing monomer with the other monomer copolymerizable therewith. The copolymer is readily obtained by adding a radical polymerization initiator to a 5 solution of the monomers, followed by heating to effect reaction. The initiator is selected from peroxides such as dicumyl peroxide and benzoyl peroxide and azo compounds such as azobisisobutyronitrile.
Component (B)
Component (B) is a hydrolytic condensate (final reaction product) of the reaction product of a xcex2-diketone with a mixture (b-1) and/or a mixture of a xcex2-diketone with a mixture (b-1). The mixture (b-1) contains a titanium tetraalkoxide and a metal alkoxide of the formula: M(OR)n wherein M is at least one metal selected from the group consisting of Zr, Fe, Al, Zn, In, Cu, Si, Sn, W, and Mg, n is the valence of the metal, and R is an alkyl group of 1 to 10 carbon atoms or hydrogen.
The final reaction product is (1) a hydrolytic condensate obtained by reacting in a solvent the mixture (b-1) with a xcex2-diketone of the general formula: R1COCH2COR2 wherein R1 and R2 are alkyl groups of 1 to 6 carbon atoms and may be the same or different, followed by hydrolytic condensation; or (2) a hydrolytic condensate obtained by subjecting the mixture (b-1) to hydrolytic condensation in a solvent containing a xcex2-diketone of the general formula: R1COCH2COR2 wherein R1 and R2 are as defined above.
Illustrative examples of the titanium alkoxide and the metal alkoxide M(OR)n include tetra-i-propoxytitanium, tetra-n-butoxytitanium, tetrakis(2-ethylhexyloxy)titanium, tetrastearyloxytitanium, tetraethoxyzirconium, tetra-i-propoxyzirconium, tetra-n-butoxyzirconium, tetra-sec-butoxyzirconium, tetra-t-butoxyzrconium, tetra-n-pentoxyzirconium, tetrakis(2-ethylhexyloxy)zirconium, tetrastearyloxyzirconium, triethoxyaluminum, tri-i-propoxyaluminum, mono-sec-butoxy-propoxyaluminum, tri-sec-butoxy-aluminum, triethoxyiron (III), tri-i-propoxyiron (III), tri-i-propoxyindium, pentaethoxytungsten, hexaethoxytungsten, tetramethoxysilane, and tetraethoxysilane. Oligomers of these titanium alkoxides and metal alkoxides are also useful. In the mixture (b-1) of titanium tetraalkoxide and metal alkoxide M(OR)n, titanium and the other metal are preferably contained in such amounts that there are present 100 parts by weight calculated as TiO2 of the titanium tetraalkoxide and 0.01 to 50 parts, especially 0.1 to 30 parts by weight calculated as oxide of the metal alkoxide. If the amount of the metal alkoxide other than titanium is more than 50 parts, the UV-absorbing effects of titanium can be retarded. If the metal alkoxide M(OR)n is not present at all, the titanium tetraalkoxide alone imparts insufficient weather resistance and abrasion resistance.
The xcex2-diketone is of the general formula:
R1COCH2COR2 
wherein R1 and R2, which may be the same or different, are alkyl groups of 1 to 6 carbon atoms. Exemplary groups of R1 and R2 are methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, t-butyl, and hexyl. Illustrative examples of the xcex2-diketone include acetylacetone, 2,4-hexanedione, 2,4-heptanedione, 3,5-heptanedione, 2,4-octanedione, 2,4-nonanedione, 5-methylhexanedione, 2,2,6,6-tetramethyl-3,5-heptanedione. Of these, acetylacetone is most preferred. These xcex2-diketones may be used alone or in admixture of two or more.
In the practice of the invention, component (B) or final reaction product is obtained (1) by reacting in a solvent the mixture (b-1) with the xcex2-diketone, followed by hydrolytic condensation; or (2) by subjecting the mixture (b-1) to hydrolytic condensation in a solvent containing the xcex2-diketone.
The blending ratio of the mixture (b-1) and the xcex2-diketone is preferably such that there are 1 mol of the mixture (b-1) and 0.5 to 2 mol, more preferably 0.7 to 1.0 mol of the xcex2-diketone. If the molar ratio of xcex2-diketone to mixture (b-1) is less than 0.5, gelation can occur or stability be exacerbated during the subsequent hydrolytic condensation. If the molar ratio of xcex2-diketone to mixture (b-1) is more than 2, the subsequent hydrolytic condensation can be retarded, sometimes failing to provide an appropriate coating composition or inviting an economical disadvantage.
The solvents used herein are preferably alcohols and low-boiling organic solvents having a boiling point of lower than 120xc2x0 C. The alcohols are monohydric alcohols and dihydric alcohols. Of the monohydric alcohols, saturated aliphatic alcohols having 1 to 8 carbon atoms are preferred. Suitable alcohols are exemplified by methanol, ethanol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol monobutyl ether, and ethylene glycol monoethyl ether acetate. Exemplary low-boiling organic solvents having a boiling point of lower than 120xc2x0 C.are acetone, methyl ethyl ketone and tetrahydrofuran.
In procedure (1), the mixture (b-1) is first reacted with the xcex2-diketone. The reaction is preferably effected at a temperature of about 20 to 120xc2x0 C. for a time of about 1 to 10 hours. The resulting reaction product is a mixture of compounds of the following formula (b-2). 
Herein, M1 is Ti, Zr, Fe, Al, Zn, In, Cu, Si, Sn, W or Mg. The inclusion of a compound of formula (b-2) wherein M1 is Ti in the mixture is essential. R is as defined above. The letter c is from 2 to 3.5 on the average, d is from 0.5 to 2 on the average, and c+d=n wherein n is the valence of the metal M1.
It is noted that the compounds of formula (b-2) or the mixture thereof may be commercial products if any. In the mixture of compounds of formula (b-2), there can be co-present a titanium tetraalkoxide and/or another metal alkoxide M(OR)n.
In procedures (1) and (2), hydrolytic condensation is preferably effected by adding 3.1 to 15 molar equivalents of water is added per molar equivalent of the mixture (b-1). A more appropriate amount of water is 3.4 to 8.0 molar equivalents. With less than 3.1 molar equivalents of water, the reaction product may have a weak UV absorbing capability probably because of failure to take microparticulate shape. More than 15 molar equivalents of water can cause gelation.
For the hydrolytic condensation, reaction is preferably carried out at a temperature of about 20 to 120xc2x0 C. for a time of about 1 to 30 hours. More preferably, reaction is preferably carried out at a temperature of about 60 to 90xc2x0 C. for a time of about 5 to 20 hours. Further preferably, hydrolytic condensation is carried out under acidic or basic conditions. To this end, any of well-known acidic catalyst and basic catalysts may be used. Suitable acidic catalysts are acidic hydrogen halides, carboxylic acids and sulfonic acids. Illustrative examples are hydrochloric acid, nitric acid, sulfuric acid, acetic acid, and maleic acid. Preferred basic catalysts are amine catalysts, with illustrative examples including ammonia, dimethylamine and diethylamine.
The thus obtained hydrolytic condensate or final reaction product as component (B) is in the form of metal oxide microparticulates having a mean particle size of up to 100 nm and bearing xcex2-keto ester groups (xcex2-diketone groups) and preferably capable of absorbing ultraviolet radiation of shorter than 350 nm.
In the coating composition of the invention, there are present 100 parts by weight as solids of component (A) and 0.1 to 50 parts by weight of effective solids of the hydrolytic condensate (B). An appropriate amount of the hydrolytic condensate (B) is at least 1 part, especially at least 2 parts by weight, but up to 50 parts, especially up to 30 parts by weight. More than 50 parts by weight of (B) is economically disadvantageous whereas less than 0.1 part by weight of (B) fails to achieve the desired weather and abrasion resistance.
Component (C)
In the coating composition of the invention, a microparticulate inorganic oxide may be blended as an optional component (C). This component is also designated an inorganic UV absorber since it is a microparticulate inorganic oxide capable of absorbing detrimental light rays with a wavelength of up to 400 nm which can cause decomposition and degradation of organic compounds. Since oxides of cerium and zinc have an ability to absorb light rays of up to 400 nm in wavelength, the microparticulate inorganic oxide must contain at least one of cerium and zinc. If necessary, a metal oxide other than the above-described ones is added to the inorganic oxide particles in any desired manner for the purpose of stabilizing the particles or improving weather resistance, and as long as the light absorbing ability is not impaired. The manner of adding the other metal oxide includes simple addition, mechanical adsorption of the other metal oxide to the periphery of inorganic oxide particles, coating of inorganic oxide particles on their surface with a thin film of the other metal oxide, formation of mixed crystals by the sol-gel method, and doping of inorganic oxide particles with the other metal oxide in crystal form. Examples of the other metal include Si (silica), Al (alumina), Sn (tin oxide), Zr (zirconia), Sb (antimony oxide), Fe (iron oxide), and rare earth metals (rare earth metal oxides) though not limited thereto. Of these, oxides of Si, Al, Sn and Zr are preferred.
The inorganic oxide particles (C) should preferably have a particle size of 1 to 300 nm, more preferably 1 to 200 nm. Particles with a size of greater than 300 nm may adversely affect light transmission. Particles with a size of less than 1 nm are inadequate since they are unstable and difficult to prepare. The inorganic oxide particles may be used in the form of powder, water dispersion or organic solvent dispersion.
In the coating composition, preferably 0.1 to 100 parts, more preferably 1 to 80 parts by weight of the inorganic oxide particles (C) is blended with 100 parts by weight as solids of component (A). Less than 0.1 part of component (C) may fail to achieve its additive effects or its combined effects with component (B). Blending of more than 100 parts of component (C) may adversely affect film strength and film transparency and is uneconomical.
Component (D)
In the coating composition, colloidal silica is preferably blended as an optional component (D). Colloidal silica is blended in an amount of 1 to 200 parts, especially 10 to 150 parts by weight of per 100 parts by weight of component (A). One exemplary blending procedure is by mixing 20 to 90 parts by weight of component (A) with 10 to 80 parts by weight as solids of a colloidal silica containing silica fines having a particle size of 1 to 100 nm to a total amount of 100 parts by weight. The mixture is diluted with alcohol, water or water-miscible solvent to a nonvolatile concentration of 15 to 20% by weight. The dilution is ripened at room temperature for about 3 to 5 days or at 40 to 60xc2x0 C. for about 10 to 15 hours. The term xe2x80x9ccolloidal silicaxe2x80x9d is a dispersion of silica fines in water or an alcohol such as methanol, ethanol, isobutanol or diacetone alcohol.
Also, upon the above-described hydrolysis, the colloidal silica may be added along with the acid catalyst. To the colloidal silica-laden coating composition, a buffer solution and a curing catalyst are preferably added so as to provide adequate abrasion resistance.
Examples of the curing catalyst include dimethylamine, acetic ethanol amine, formic dimethylaniline, benzoic acid, tetraethylammonium salts, sodium acetate, sodium propionate, sodium formate, trimethylammonium benzoyl acetate, tetra-i-propoxytitanium, tetra-n-butoxytitanium, aluminum triisobutoxide, aluminum triisopropoxide, aluminum acetylacetonate, aluminum perchlorate, aluminum chloride, cobalt octylate, cobalt acetylacetonate, zinc octylate, zinc acetylacetonate, iron acetylacetonate, tin acetylacetonate, dibutyltin octylate, and dibutyltin laurate. An appropriate amount of the curing catalyst added is 0.02 to 0.4 part by weight per 100 parts by weight as solids of the colloidal silica-laden protective coating composition.
From the standpoint of insuring stability, the coating composition is preferably adjusted to pH 2 to 7, at which silanol groups remain stable, and especially pH 3 to 6. The buffer used for pH adjustment may be a combination of acidic and basic compounds, for example, a combination of acetic acid and sodium acetate and a combination of disodium hydrogen phosphate and citric acid.
If the coating composition has a too low viscosity to apply and thus forms only a thin coating, an acrylic polymer may be added as a component capable of imparting flexibility without detracting from adhesion. Such useful acrylic polymers include poly(alkyl methacrylates) and poly(alkyl acrylates) such as poly(methyl methacrylate), poly(butyl methacrylate), and poly(butyl acrylate), and copolymers thereof. These acrylic polymers are effective for imparting flexibility to the primer coating composition using the organic copolymer (A-1) without detracting from adhesion. The amount of the acrylic polymer added is desirably limited to 30% by weight or less based on the entire primer coating composition since more than 30% by weight of the acrylic polymer can preclude the composition from heat curing.
In the coating composition, a compound containing a nitrogen atom and an alkoxysilyl group in a molecule may be added for the purposes of assisting the composition in forming a satisfactory bond having water resistance, and fixing within the coating the optional photo-stabilizer by crosslinking with alkoxysilyl groups in the organic copolymer (A-2). Preferably the compound contains at least one nitrogen atom and at least two alkoxysilyl groups in a molecule.
Preferred examples of the compound used herein include an amino group-containing alkoxysilane, amide group-containing alkoxysilane, one obtained by reacting an amino group-containing alkoxysilane with an epoxy group-containing alkoxysilane and a silylating agent and amidating the reaction product, the reaction product of an amino group-containing alkoxysilane with a polyfunctional (meth)acrylic compound, the reaction product of an amino group-containing alkoxysilane with a (meth)acrylic compound, the reaction product of an amino group-containing alkoxysilane with a (meth)acrylic group-containing alkoxysilane, the reaction product of a polyamine compound with a (meth)acrylic group-containing alkoxysilane, one obtained by reacting an amino group-containing alkoxysilane with a polyfunctional isocyanate compound and amidating the reaction product, one obtained by reacting an amino group-containing alkoxysilane with an isocyanate group-containing alkoxysilane and amidating the reaction product, and the reaction product of a thiol group-containing alkoxysilane with an isocyanate group-containing alkoxysilane. Of these, preferred is the one obtained by reacting an amino group-containing alkoxysilane with an epoxy group-containing alkoxysilane and a silylating agent and amidating the reaction product.
Illustrative examples of the components used herein are described. Examples of the amino group-containing alkoxysilane include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, 3-(trimethoxysilylpropyl)-aminopropyltrimethoxysilane, 3-(triethoxysilylpropyl)-aminopropyltriethoxysilane, 2-(trimethoxysilylpropyl)-aminoethyl-3-aminopropyltrimethoxysilane, and 2-(triethoxysilylpropyl)aminoethyl-3-aminopropyltriethoxysilane.
Examples of the amide group-containing alkoxysilane include ureidopropyltrimethoxysilane, ureidopropyltriethoxysilane, ureidopropylmethyldimethoxysilane, and ureidopropylmethyldiethoxysilane.
The process of obtaining the amide compound by reacting an amino group-containing alkoxysilane with an epoxy group-containing alkoxysilane and a silylating agent and amidating the reaction product is described below. The amino group-containing alkoxysilane is as exemplified above although N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane are preferred for adhesion and operation. Illustrative examples of the epoxy group-containing alkoxysilane include xcex3-glycidoxypropyltrimethoxysilane, xcex3-glycidoxypropylmethyldimethoxysilane, xcex3-glycidoxypropyltriethoxysilane, xcex3-glycidoxypropylmethyldiethoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, xcex2-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and xcex2-(3,4-epoxycyclohexyl)ethylmethyldiethoxysilane. From the standpoints of reactivity and ease of operation, the preferred silane compounds are xcex3-glycidoxypropyltrimethoxysilane, xcex3-glycidoxypropylmethyldimethoxysilane, and xcex2-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane.
Examples of the silylating agent include hexamethyldisilazane, N,Nxe2x80x2-bis(trimethylsilyl)formamide and N,Nxe2x80x2-bis(trimethylsilyl)urea. When the amino group-containing alkoxysilane reacts with an epoxy group-containing alkoxysilane, the silylating agent serves to protect the OH groups generated by the reaction for preventing reaction between OH groups and alkoxysilyl groups, thereby precluding a change with time of the reaction product.
Reaction of the amino group-containing alkoxysilane with the epoxy group-containing alkoxysilane and the silylating agent may be effected by adding dropwise the epoxy group-containing alkoxysilane to a mixture of the amino group-containing alkoxysilane and the silylating agent and heating the mixture for reaction. Alternatively, the amino group-containing alkoxysilane is reacted with the epoxy group-containing alkoxysilane, and the silylating agent is added to the reaction product for further reaction.
In this reaction, the amino group-containing alkoxysilane and the epoxy group-containing alkoxysilane are preferably used in such amounts that the molar ratio of epoxy groups to amino (xe2x95x90Nxe2x80x94H) groups may range from 0.3/1 to 1.2/1. If the molar ratio of epoxy/amino is less than 0.3, only a less number of alkoxy groups per molecule participate in crosslinking, leading to short cure, and the entire molecule is not spread, leading to a weak surface bond. If the molar ratio of epoxy/amino is more than 1.2, amino (xe2x95x90Nxe2x80x94H) groups which can be amidated during subsequent amidation step become few, exacerbating water-resistant bond.
The reaction product is then amidated. For amidation, the reaction product may be reacted with a carboxylic acid halide, acid anhydride or acid isopropenyl ester such as acetic chloride, acetic bromide, propionic chloride, acetic anhydride, isopropenyl acetate or benzoyl chloride.
In the coating composition, 0.5 to 20 parts by weight of the compound is preferably blended per 100 parts by weight of component (A). An excessive amount of the compound may result in a coating having a too high crosslinked density, a high hardness, and rather poor adhesion.
In the coating composition, a photo-stabilizer having at least one cyclic hindered amine structure in a molecule may be added for improving weather resistance. The photo-stabilizer used herein should preferably be fully soluble in the solvent of the coating composition, compatible with the organic copolymer (A-2) if used, and low volatile. In the coating composition, 2.6 to 10 parts by weight of the photo-stabilizer is preferably blended per 100 parts by weight of component (A). More than 10 parts of the photo-stabilizer detracts from adhesion of a coating.
Illustrative examples of the photo-stabilizer include 3-dodecyl-1-(2,2,6,6-tetramethyl-4-piperidinyl)pyrrolidine-2,5-dione, N-methyl-3-dodecyl-1-(2,2,6,6-tetramethyl-4-piperidinyl)pyrrolidine-2,5-dione, N-acetyl-3-dodecyl-1-(2,2,6,6-tetramethyl-4-piperidinyl)pyrrolidine-2,5-dione, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, tetrakis(2,2,6,6-tetramethyl-4-piperidyl) 1,2,3,4-butanetetracarboxylate, tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl) 1,2,3,4-butanetetracarboxylate, a condensate of 1,2,3,4-butanetetracarboxylic acid with 2,2,6,6-tetramethylpiperidinol and tridecanol, 8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro[4,5]decane-2,4-dione, a condensate of 1,2,3,4-butanetetracarboxylic acid with 1,2,6,6-tetramethyl-4-piperidinol and xcex2,xcex2,xcex2,xcex2xe2x80x2-tetramethyl-3,9-(2,4,8,10-tetraoxaspiro[5,5]undecane)diethanol, and a condensate of 1,2,3,4-butanetetracarboxylic acid with 2,2,6,6-tetramethyl-4-piperidinol and xcex2,xcex2,xcex2,xcex2xe2x80x2-tetramethyl-3,9-(2,4,8,10-tetraoxaspiro[5,5]undecane)diethanol. For the purpose of fixing the photo-stabilizer, there may be also used silyl-modified photo-stabilizers as disclosed in JP-B 61-56187, for example, 2,2,6,6-tetramethylpiperidino-4-propyltrimethoxysilane, 2,2,6,6-tetramethylpiperidino-4-propylmethyldimethoxysilane, 2,2,6,6-tetramethylpiperidino-4-propyltriethoxysilane, and 2,2,6,6-tetramethylpiperidino-4-propylmethyldiethoxysilane as well as (partial) hydrolyzates thereof. These photo-stabilizers may be used in admixture of two or more.
In the coating composition, a conventional ultraviolet absorber which has not been silyl modified may be added insofar as no detrimental effect is exerted. Such UV absorbers are preferably organic UV absorbers compatible with component (A), especially organic copolymer (A-2). Derivatives of compounds having a hydroxybenzophenone, benzotriazole, cyanoacrylate or triazine main skeleton are especially preferred. Also acceptable are polymers such as vinyl polymers having such a UV absorber incorporated on a side chain. Exemplary UV absorbers are 2,4xe2x80x2-dihydroxybenzophenone, 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, 2-hydroxy-4-n-octoxybenzophenone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2-hydroxy-4-n-benzyloxybenzophenone, 2,2xe2x80x2-dihydroxy-4,4xe2x80x2-dimethoxybenzophenone, 2,2xe2x80x2-dihydroxy-4,4xe2x80x2-diethoxybenzophenone, 2,2xe2x80x2-dihydroxy-4,4xe2x80x2-dipropoxybenzophenone, 2,2xe2x80x2-dihydroxy-4,4xe2x80x2-dibutoxybenzophenone, 2,2xe2x80x2-dihydroxy-4-methoxy-4xe2x80x2-propoxybenzophenone, 2,2xe2x80x2-dihydroxy-4-methoxy-4xe2x80x2-butoxybenzophenone, 2,3,4-trihydroxybenzophenone, 2-(2-hydroxy-5-t-methylphenyl)benzotriazole, 2-(2-hydroxy-5-t-octylphenyl)benzotriazole, 2-(2-hydroxy-3,5-di-t-butylphenyl)benzotriazole, ethyl-2-cyano-3,3-diphenyl acrylate, 2-ethylhexyl-2-cyano-3,3-diphenyl acrylate, 2-(2-hydroxy-4-hexyloxyphenyl)-4,6-diphenyltriazine, 4-(2-acryloxyethoxy)-2-hydroxybenzophenone polymer, and 2-(2xe2x80x2-hydroxy-5xe2x80x2-methacryloxyethylphenyl)-2H-benzotriazole polymer. Of these, 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone is most preferred from the standpoints of compatibility with the primer coating composition using component (A-2) and volatility. These organic UV absorbers may be used in admixture of two or more.
On use, the coating composition is diluted with a solvent. Useful solvents include diacetone alcohol, propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, isobutyl alcohol, isopropyl alcohol, n-butyl alcohol, n-propyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetyl acetone, ethyl acetate, butyl acetate, xylene, and toluene. The primer coating composition is generally diluted with the solvent into a solution containing 5 to 10% by weight of the organic copolymer (A-2) prior to use.
In the coating composition, well-known additives commonly used in conventional coating compositions, such as leveling agents, are blended if necessary.
The coating composition is useful in protecting surfaces of various articles, especially plastic articles. Specifically the coating composition is applied to an article substrate to form a protective coating thereon. The plastic article substrates to which the composition is applicable include those of polycarbonate, polystyrene, modified acrylic resins, urethane resins, thiourethane resins, polycondensates of halogenated bisphenol A and ethylene glycol, acrylic urethane resins, halogenated aryl group-containing acrylic resins, and sulfur-containing resins. The benefits become more outstanding when the coating composition is applied to transparent plastic substrates, and especially polycarbonate resins.
When the coating composition is applied to an article substrate to form a protective coating thereon, it is preferred that a primer layer intervenes between the substrate and the coating in order to enhance the adhesion to the substrate, especially plastic substrate. The primer coating composition used herein to form the primer layer is preferably selected from (i) primer coating compositions comprising components (A-2) and (B); (ii) primer coating compositions comprising component (A-2), free of component (B); and (iii) primer coating compositions comprising well-known organic resins commonly used as the primer, for example, thermosetting acrylic resins, moisture-curable acrylic resins, thermoplastic acrylic resins, silane or siloxane-modified acrylic resins, and urethane resins. Of these, the primer coating compositions (i) comprising components (A-2) and (B) are preferred.
The primer coating composition in solution form is applied to a surface of a plastic substrate, typically a plastic film, which has been cleaned, whereupon the diluting solvent is evaporated off at room temperature or elevated temperature, leaving a dry undercoat of about 1 to 10 xcexcm, preferably about 2 to 5 xcexcm thick. The organic solvent dilution should preferably have a viscosity of about 5 to 30 centistokes. A dilution with a viscosity of less than 5 centistokes would be difficult to form a thick coat whereas a dilution with a viscosity of more than 30 centistokes would be difficult to handle and apply. To the composition, a fluorochemical or silicone surfactant may be added for leveling of the coating, and a catalytic amount of a crosslinking/curing catalyst may also be added for accelerating cure.
By covering plastic substrates such as plastic films and sheets with the cured coat or primer layer of the primer coating composition, the substrates are improved in initial adhesion, heat resistance, hot-water resistance, and weather resistance. Advantageously, a topcoat is formed on the primer coat, using a coating composition.
The coating composition for the topcoat is in the first place, the coating composition of the invention mentioned above, especially the coating composition comprising component (A-1) and (B), and in the second place, a conventional colloidal silica-laden organopolysiloxane composition. The latter composition contains a hydrolyzate or co-hydrolyzate of an organoxysilane having the general formula (2):
R7eSi(OR8)4-exe2x80x83xe2x80x83(2) 
wherein R7 is an alkyl group, aryl group, halogenated alkyl group, halogenated aryl group or alkenyl group of 1 to 10 carbon atoms, or an organic group having an epoxy, (meth)acryloxy, mercapto, amino or cyano group, R8 is hydrogen or a monovalent organic group of 1 to 10 carbon atoms (e.g., alkyl and alkenyl), and e is equal to 0, 1 or 2, and 5 to 70% by weight of colloidal silica obtained by dispersing silica fines with a size of 1 to 100 nm in water or alcohol (e.g., methanol, ethanol, isobutanol or diacetone alcohol). The topcoat composition is applied onto the primer coat of the primer coating composition on a plastic substrate and cured by heating, typically at a temperature of 50 to 140xc2x0 C. In this way, a top coat is formed on the plastic substrate to a high bond strength. The top coat of the inventive coating composition or conventional organo-polysiloxane composition synergistically cooperates with the primer coat of the inventive primer coating composition to accomplish high adhesion and abrasion resistance as well as excellent weather resistance and its stability due to the improved UV absorbing capability.